add SSL and ssl for gadget2 stars particles

src/snapshotgadget.cc

@@ -600,7 +600,7 @@ int CSnapshotGadgetIn<T>::read(uns::UserSelection &user_select)
           readOneArray(&im,4,compOffset);
         }
         // --> SSL block
-        if (block_name=="SSL" && this->req_bits&SSL_BIT && this->comp_bits&STARS_BIT) {
+        if ((block_name=="SSL" || block_name=="ssl") && this->req_bits&SSL_BIT && this->comp_bits&STARS_BIT) {
           this->load_bits |= SSL_BIT;
           assert((header.npart[4])>0); // stars
           ok=true;